1. Field of the Invention
The present invention relates generally to a corona discharger displacing mechanism and a grid electrode positioning mechanism, and more particularly, to a corona discharger displacing mechanism and a grid electrode positioning mechanism which are most suitable for an image forming apparatus, such as an electrostatic process copying machine, a facsimile and a laser beam printer.
2. Description of the Related Art
An image forming apparatus employing this type of corona discharger displacing mechanism generally comprises an image forming section for developing an electrostatic latent image into a toner image.
The image forming section comprises an image carrier for carrying an image to be formed and a corona discharger having a discharge wire stretched in the vicinity of the surface of the image carrier. The corona discharger is for applying a high voltage to the discharge wire from a feed component of the image forming apparatus through a high-voltage generating component, to cause the discharge wire to induce corona discharge so that the surface of the image carrier is charged.
The image carrier must be replaced frequently depending on the state of use because its service life is relatively short. Consequently, there has widely been employed a unit detachably contained in the main body of an image forming apparatus which detachably supports the image carrier. This unit has such simple operational advantages that an image carrier on the unit can be replaced with a new one by extracting the unit from the main body of the image forming apparatus when a predetermined amount of image forming operations have been performed.
On the other hand, because the discharge wire in the corona discharger is opposed to the vicinity of the image carrier, a mechanism is required to enable the replacement of the unit. Therefore, the image forming apparatus has conventionally been provided with a displacing mechanism for displacing the corona discharger to a retreat position, where the replacement or insertion and extraction of the unit is allowed, and a set position, where the discharge wire is opposed to the vicinity of the image carrier in the unit.
In order to apply the image forming apparatus of the foregoing construction for home or personal use, it is preferable that maintenance work of the unit can be performed as simply and reliably as possible.
In the foregoing construction, however, the displacing operation of the corona discharger and the replacement operation of the unit are not synchronized with each other. Accordingly, a user must individually perform the operations. This is a great burden to the user. In addition, the user frequently forgets to set the corona discharger.
Accordingly, what is really needed is a corona discharger displacing mechanism which can perform the maintenance work of a unit simply and reliably, thereby constituting the most suitable image forming apparatus for home or personal use.
Next, there may be employed an image forming section of a so-called scorotron type in the foregoing image forming apparatus.
The image forming section of a scorotron type comprises a grid electrode stretched in the vicinity of the surface of the image carrier so that the corona discharger charges the surface of an image carrier through the grid electrode (see, for example, Japanese Unexamined Patent Publication No. 59-56381).
The grid electrode must be constructed so as to be detachable relatively easily for cleaning or replacement. Conventionally, in the image forming apparatus of a scorotron type, the grid electrode has also been detachably mounted on a unit, similar to the image carrier.
More specifically, the image forming apparatus of scorotron type has a unit which is integrally provided with a pair of supporting portions for holding the image carrier. Supporting portions have predetermined parts to which are respectively fixed both ends of the grid electrode corresponding to the support portions. The unit is further provided with a contact portion onto which the grid electrode is pressed so as to apply a predetermined tensile force to the grid electrode in co-operation with a fixing member.
In order to improve the charging performance of the image forming apparatus of the foregoing construction, it is preferable that the opposed distance between the grid electrode and the surface of the image carrier is kept uniform.
In the conventional construction, however, there is only provided the contact portion onto which the grid electrode is pressed. Accordingly, it is difficult to adjust the grid electrode to the contact portion and to position the grid electrode on the surface of the image carrier. Therefore, assembling error often occurred in the opposed distance between the grid electrode and the image carrier, thereby being a burden to the manufacturing operator.
Accordingly, what is really needed is a grid electrode positioning mechanism capable of positioning a grid electrode on the surface of an image carrier reliably, thereby exhibiting high charging performance.